[PATCH] kdump: add a missing notifier before crashing

["Akiyama, Nobuyuki" <akiyama.nobuyuk@jp.fujitsu.com>]

Hi all,

The attached patch adds a missing notifier before crashing.
This patch is remade to follow the former discussions.
The change is that a notifier calling becomes optional.
Please refer to the following thread for details:

http://lists.osdl.org/pipermail/fastboot/2006-May/003018.html

Description:
We don't have a simple and light weight way to know the kernel dies.
The panic notifier does not be called if kdump is activated
because crash_kexec() does not return, and there is no mechanism to
notify of a crash before crashing by SysRq-c.
Although notify_die() exists, the function depends on architecture.
If notify_die() is added in panic and SysRq respectively like
existing implementation, the code will be ugly.
I think that adding a generic hook in crash_kexec() is better to
simplify the code.

This new notifier is useful, especially for a clustering system.
On a mission critical system, failover need to start within a few
milli-second. The notifier could be called on 2nd kernel, but it is
no use because it takes the time of second order to boot up.

The attached patch is against 2.6.17-rc6-git5.
I tested on i386-box.

Thanks,

Akiyama, Nobuyuki

Signed-off-by: Akiyama, Nobuyuki <akiyama.nobuyuk@jp.fujitsu.com>
---

 Documentation/filesystems/proc.txt |   11 +++++++++++
 arch/i386/kernel/traps.c           |    4 ++--
 arch/powerpc/kernel/traps.c        |    2 +-
 arch/x86_64/kernel/traps.c         |    4 ++--
 drivers/char/sysrq.c               |    2 +-
 include/linux/kexec.h              |   12 ++++++++++--
 include/linux/sysctl.h             |    1 +
 kernel/kexec.c                     |   18 +++++++++++++++++-
 kernel/panic.c                     |    2 +-
 kernel/sysctl.c                    |   11 +++++++++++
 10 files changed, 57 insertions(+), 10 deletions(-)

diff -Nurp linux-2.6.17-rc6-git5/Documentation/filesystems/proc.txt linux-2.6.17-rc6-git5.mod/Documentation/filesystems/proc.txt
--- linux-2.6.17-rc6-git5/Documentation/filesystems/proc.txt	2006-06-14 16:25:26.000000000 +0900
+++ linux-2.6.17-rc6-git5.mod/Documentation/filesystems/proc.txt	2006-06-15 14:48:59.000000000 +0900
@@ -1130,6 +1130,17 @@ If a system hangs up, try pressing the N
    And NMI watchdog will be disabled when the value in this file is set to
    non-zero.
 
+kdump_safe
+----------
+
+The value in this file affects behavior of a notifier before kdump. When the
+value is non-zero(default), the notifier is not called before crashing. If the
+notifier is expected to be called before crashing, set zero.
+
+[NOTE]
+   The notifier may be hung and kdump may be stalled because the notifier is
+   usually called under panic state. The value of this file should be decided
+   by the policy of system usage.  
 
 2.4 /proc/sys/vm - The virtual memory subsystem
 -----------------------------------------------
diff -Nurp linux-2.6.17-rc6-git5/arch/i386/kernel/traps.c linux-2.6.17-rc6-git5.mod/arch/i386/kernel/traps.c
--- linux-2.6.17-rc6-git5/arch/i386/kernel/traps.c	2006-06-14 16:25:26.000000000 +0900
+++ linux-2.6.17-rc6-git5.mod/arch/i386/kernel/traps.c	2006-06-14 16:02:46.000000000 +0900
@@ -414,7 +414,7 @@ void die(const char * str, struct pt_reg
 		return;
 
 	if (kexec_should_crash(current))
-		crash_kexec(regs);
+		crash_kexec(CRASH_ON_DIE, regs, NULL);
 
 	if (in_interrupt())
 		panic("Fatal exception in interrupt");
@@ -665,7 +665,7 @@ void die_nmi (struct pt_regs *regs, cons
 	*/
 	if (!user_mode_vm(regs)) {
 		current->thread.trap_no = 2;
-		crash_kexec(regs);
+		crash_kexec(CRASH_ON_DIE, regs, NULL);
 	}
 
 	do_exit(SIGSEGV);
diff -Nurp linux-2.6.17-rc6-git5/arch/powerpc/kernel/traps.c linux-2.6.17-rc6-git5.mod/arch/powerpc/kernel/traps.c
--- linux-2.6.17-rc6-git5/arch/powerpc/kernel/traps.c	2006-06-14 16:25:27.000000000 +0900
+++ linux-2.6.17-rc6-git5.mod/arch/powerpc/kernel/traps.c	2006-06-14 16:02:46.000000000 +0900
@@ -132,7 +132,7 @@ int die(const char *str, struct pt_regs 
 	if (!crash_dump_start && kexec_should_crash(current)) {
 		crash_dump_start = 1;
 		spin_unlock_irq(&die_lock);
-		crash_kexec(regs);
+		crash_kexec(CRASH_ON_DIE, regs, NULL);
 		/* NOTREACHED */
 	}
 	spin_unlock_irq(&die_lock);
diff -Nurp linux-2.6.17-rc6-git5/arch/x86_64/kernel/traps.c linux-2.6.17-rc6-git5.mod/arch/x86_64/kernel/traps.c
--- linux-2.6.17-rc6-git5/arch/x86_64/kernel/traps.c	2006-06-14 16:25:27.000000000 +0900
+++ linux-2.6.17-rc6-git5.mod/arch/x86_64/kernel/traps.c	2006-06-14 16:02:46.000000000 +0900
@@ -445,7 +445,7 @@ void __kprobes __die(const char * str, s
 	printk_address(regs->rip); 
 	printk(" RSP <%016lx>\n", regs->rsp); 
 	if (kexec_should_crash(current))
-		crash_kexec(regs);
+		crash_kexec(CRASH_ON_DIE, regs, NULL);
 }
 
 void die(const char * str, struct pt_regs * regs, long err)
@@ -469,7 +469,7 @@ void __kprobes die_nmi(char *str, struct
 	printk(str, safe_smp_processor_id());
 	show_registers(regs);
 	if (kexec_should_crash(current))
-		crash_kexec(regs);
+		crash_kexec(CRASH_ON_DIE, regs, NULL);
 	if (panic_on_timeout || panic_on_oops)
 		panic("nmi watchdog");
 	printk("console shuts up ...\n");
diff -Nurp linux-2.6.17-rc6-git5/drivers/char/sysrq.c linux-2.6.17-rc6-git5.mod/drivers/char/sysrq.c
--- linux-2.6.17-rc6-git5/drivers/char/sysrq.c	2006-06-14 16:25:28.000000000 +0900
+++ linux-2.6.17-rc6-git5.mod/drivers/char/sysrq.c	2006-06-14 16:02:46.000000000 +0900
@@ -99,7 +99,7 @@ static struct sysrq_key_op sysrq_unraw_o
 static void sysrq_handle_crashdump(int key, struct pt_regs *pt_regs,
 				struct tty_struct *tty)
 {
-	crash_kexec(pt_regs);
+	crash_kexec(CRASH_ON_SYSRQ, pt_regs, NULL);
 }
 static struct sysrq_key_op sysrq_crashdump_op = {
 	.handler	= sysrq_handle_crashdump,
diff -Nurp linux-2.6.17-rc6-git5/include/linux/kexec.h linux-2.6.17-rc6-git5.mod/include/linux/kexec.h
--- linux-2.6.17-rc6-git5/include/linux/kexec.h	2006-03-20 14:53:29.000000000 +0900
+++ linux-2.6.17-rc6-git5.mod/include/linux/kexec.h	2006-06-14 16:02:46.000000000 +0900
@@ -1,12 +1,18 @@
 #ifndef LINUX_KEXEC_H
 #define LINUX_KEXEC_H
 
+/* crash type for notifier */
+#define CRASH_ON_PANIC		1
+#define CRASH_ON_DIE		2
+#define CRASH_ON_SYSRQ		3
+
 #ifdef CONFIG_KEXEC
 #include <linux/types.h>
 #include <linux/list.h>
 #include <linux/linkage.h>
 #include <linux/compat.h>
 #include <linux/ioport.h>
+#include <linux/notifier.h>
 #include <asm/kexec.h>
 
 /* Verify architecture specific macros are defined */
@@ -103,9 +109,11 @@ extern asmlinkage long compat_sys_kexec_
 #endif
 extern struct page *kimage_alloc_control_pages(struct kimage *image,
 						unsigned int order);
-extern void crash_kexec(struct pt_regs *);
+extern void crash_kexec(int, struct pt_regs *, void *);
 int kexec_should_crash(struct task_struct *);
 extern struct kimage *kexec_image;
+extern struct raw_notifier_head crash_notifier_list;
+extern int kdump_safe;
 
 #define KEXEC_ON_CRASH  0x00000001
 #define KEXEC_ARCH_MASK 0xffff0000
@@ -133,7 +141,7 @@ extern note_buf_t *crash_notes;
 #else /* !CONFIG_KEXEC */
 struct pt_regs;
 struct task_struct;
-static inline void crash_kexec(struct pt_regs *regs) { }
+static inline void crash_kexec(int type, struct pt_regs *regs, void *v) { }
 static inline int kexec_should_crash(struct task_struct *p) { return 0; }
 #endif /* CONFIG_KEXEC */
 #endif /* LINUX_KEXEC_H */
diff -Nurp linux-2.6.17-rc6-git5/include/linux/sysctl.h linux-2.6.17-rc6-git5.mod/include/linux/sysctl.h
--- linux-2.6.17-rc6-git5/include/linux/sysctl.h	2006-06-14 16:25:35.000000000 +0900
+++ linux-2.6.17-rc6-git5.mod/include/linux/sysctl.h	2006-06-14 16:02:46.000000000 +0900
@@ -148,6 +148,7 @@ enum
 	KERN_SPIN_RETRY=70,	/* int: number of spinlock retries */
 	KERN_ACPI_VIDEO_FLAGS=71, /* int: flags for setting up video after ACPI sleep */
 	KERN_IA64_UNALIGNED=72, /* int: ia64 unaligned userland trap enable */
+	KERN_KDUMP_SAFE=73,	/* int: crash notifier flag */
 };
 
 
diff -Nurp linux-2.6.17-rc6-git5/kernel/kexec.c linux-2.6.17-rc6-git5.mod/kernel/kexec.c
--- linux-2.6.17-rc6-git5/kernel/kexec.c	2006-03-20 14:53:29.000000000 +0900
+++ linux-2.6.17-rc6-git5.mod/kernel/kexec.c	2006-06-14 16:02:46.000000000 +0900
@@ -20,6 +20,8 @@
 #include <linux/syscalls.h>
 #include <linux/ioport.h>
 #include <linux/hardirq.h>
+#include <linux/module.h>
+#include <linux/notifier.h>
 
 #include <asm/page.h>
 #include <asm/uaccess.h>
@@ -27,6 +29,11 @@
 #include <asm/system.h>
 #include <asm/semaphore.h>
 
+
+RAW_NOTIFIER_HEAD(crash_notifier_list);
+EXPORT_SYMBOL(crash_notifier_list);
+int kdump_safe = 1;
+
 /* Per cpu memory for storing cpu states in case of system crash. */
 note_buf_t* crash_notes;
 
@@ -1040,7 +1047,15 @@ asmlinkage long compat_sys_kexec_load(un
 }
 #endif
 
-void crash_kexec(struct pt_regs *regs)
+static inline void notify_crash(int type, void *v)
+{
+#ifdef CONFIG_SYSCTL
+	if (!kdump_safe)
+		raw_notifier_call_chain(&crash_notifier_list, type, v);
+#endif
+}
+
+void crash_kexec(int type, struct pt_regs *regs, void *v)
 {
 	struct kimage *image;
 	int locked;
@@ -1061,6 +1076,7 @@ void crash_kexec(struct pt_regs *regs)
 			struct pt_regs fixed_regs;
 			crash_setup_regs(&fixed_regs, regs);
 			machine_crash_shutdown(&fixed_regs);
+			notify_crash(type, v);
 			machine_kexec(image);
 		}
 		xchg(&kexec_lock, 0);
diff -Nurp linux-2.6.17-rc6-git5/kernel/panic.c linux-2.6.17-rc6-git5.mod/kernel/panic.c
--- linux-2.6.17-rc6-git5/kernel/panic.c	2006-06-14 16:25:35.000000000 +0900
+++ linux-2.6.17-rc6-git5.mod/kernel/panic.c	2006-06-14 16:02:46.000000000 +0900
@@ -85,7 +85,7 @@ NORET_TYPE void panic(const char * fmt, 
 	 * everything else.
 	 * Do we want to call this before we try to display a message?
 	 */
-	crash_kexec(NULL);
+	crash_kexec(CRASH_ON_PANIC, NULL, buf);
 
 #ifdef CONFIG_SMP
 	/*
diff -Nurp linux-2.6.17-rc6-git5/kernel/sysctl.c linux-2.6.17-rc6-git5.mod/kernel/sysctl.c
--- linux-2.6.17-rc6-git5/kernel/sysctl.c	2006-06-14 16:25:35.000000000 +0900
+++ linux-2.6.17-rc6-git5.mod/kernel/sysctl.c	2006-06-14 16:02:46.000000000 +0900
@@ -46,6 +46,7 @@
 #include <linux/syscalls.h>
 #include <linux/nfs_fs.h>
 #include <linux/acpi.h>
+#include <linux/kexec.h>
 
 #include <asm/uaccess.h>
 #include <asm/processor.h>
@@ -683,6 +684,16 @@ static ctl_table kern_table[] = {
 		.proc_handler	= &proc_dointvec,
 	},
 #endif
+#if defined(CONFIG_KEXEC)
+	{
+		.ctl_name       = KERN_KDUMP_SAFE,
+		.procname       = "kdump_safe",
+		.data           = &kdump_safe,
+		.maxlen         = sizeof (int),
+		.mode           = 0644,
+		.proc_handler	= &proc_dointvec,
+	},
+#endif
 	{ .ctl_name = 0 }
 };